If you live in London, chances are your boiler is one of the most important pieces of kit in your home. When it’s working properly, you barely think about it. When it goes wrong, though, life quickly becomes uncomfortable. Cold showers, draughty rooms, or worse still, no heating at all in the middle of winter – nobody wants that. The good news is that most boilers show warning signs before they pack up completely. Learning what to look for can save you money, hassle, and keep your home running smoothly.
Below we’ll walk through the most common boiler problems, what they mean, and how to spot them early.
1. Strange Noises – Banging, Gurgling or Whistling
Boilers aren’t meant to be noisy. A bit of humming when they fire up is normal, but loud bangs, rattles, or gurgling sounds are red flags. A whistling noise, often called “kettling”, can happen when limescale builds up inside the system, particularly in hard water areas like London. This restricts the flow of water and makes the boiler overheat.
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What to look for: sounds like a boiling kettle, clunking when the system turns on, or gurgling in the pipes.
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Why it matters: ignoring these noises can lead to more serious damage, higher energy bills, and eventually a breakdown.
2. Low Pressure
Your boiler relies on stable water pressure to push hot water around the radiators. If the pressure drops, you’ll notice lukewarm radiators or heating that doesn’t reach all corners of the house. Most modern boilers have a pressure gauge on the front. Anything below one bar usually signals an issue.
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Possible causes: leaks in the system, a recently bled radiator, or a faulty pressure relief valve.
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What to do: you can top up the pressure yourself using the filling loop, but if it keeps dropping, you’ll need an engineer to find the root cause.
3. No Hot Water or Heating
The most obvious and frustrating sign of a boiler problem is when it simply doesn’t do its job. If the radiators stay cold or the shower runs icy, the fault could lie in a number of areas:
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Broken diaphragm or airlock – parts that regulate water flow may have failed.
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Faulty thermostat – the system isn’t getting the right signal to switch on.
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Pilot light gone out – more common in older boilers.
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Frozen condensate pipe – a big issue in winter months.
Some of these issues are quick fixes, others will need professional repair.
4. Leaks and Drips
Water where it shouldn’t be is never a good sign. Leaks can come from inside the boiler casing itself or from surrounding pipework. Small drips might seem harmless, but they can cause pressure loss, rust, and eventually damage electrical components.
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What to look for: damp patches under the boiler, corrosion on nearby pipes, or a drop in pressure that doesn’t make sense.
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Next step: always call an engineer – never try to open the boiler casing yourself.
5. Radiators Not Heating Evenly
If some radiators are hot at the top but cold at the bottom, or one room stays chilly while others heat up fine, the culprit is usually sludge or trapped air. Over time, rust and debris build up in the system, reducing efficiency.
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Simple fix: bleeding radiators to release air.
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Longer-term solution: a power flush by a professional to clear out the sludge.
This not only improves comfort but also reduces strain on your boiler.
6. Pilot Light Problems
Older boilers have a small flame that burns constantly, known as the pilot light. If it keeps going out, the cause could be a faulty thermocouple, a draught blowing it out, or a deposit blocking the jet.
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Warning sign: constantly relighting the flame.
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Safety tip: if you smell gas, switch everything off and call the emergency number immediately.
Modern condensing boilers don’t usually have a visible pilot light, so this problem is becoming less common, but plenty of London homes still rely on older models.
7. Frozen Condensate Pipe
During colder months, it’s not unusual for the condensate pipe – the small plastic pipe that drains waste water outside – to freeze. When this happens, the boiler usually shuts itself down as a safety measure.
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Clue: the boiler displays an error code and refuses to start.
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Quick fix: carefully pour warm (not boiling) water over the pipe or use a hot water bottle to thaw it.
Insulating the pipe helps prevent the issue happening again.
8. Thermostat Issues
Sometimes the problem isn’t the boiler itself but the thermostat controlling it. If the heating doesn’t come on when it should, or switches off unexpectedly, the thermostat may be faulty or just need recalibrating.
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Check first: is it set to the right time and temperature?
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Upgrade option: consider a smart thermostat for better control and efficiency.
9. Unusual Smells
A healthy boiler shouldn’t give off any smell. If you notice anything unusual – especially a sulphur or gas-like odour – switch the boiler off and call an engineer straight away. Carbon monoxide is odourless but deadly, which is why every home should have a working carbon monoxide alarm near the boiler.
10. Boiler Keeps Switching Itself Off
If your boiler turns off randomly, it could be due to low pressure, a blocked condensate pipe, or poor water flow. This is more than just an inconvenience – it’s a sign the system isn’t working safely.
When to Call a Professional
While it’s fine to check pressure, bleed radiators, or thaw a frozen pipe yourself, most boiler problems should only be handled by a Gas Safe registered engineer. Attempting to fix things inside the boiler casing can be dangerous and may void your warranty.
A good rule of thumb: if in doubt, call a professional. It’s better to pay for a minor repair now than face a complete breakdown in the middle of winter.
Boilers are hardy machines, but like all appliances, they wear down over time. The key is spotting problems before they snowball. Strange noises, drops in pressure, cold radiators, or leaks are all early warning signs. Deal with them quickly and you’ll save yourself money, stress, and a lot of shivering on a cold London evening.
If your boiler is showing any of the symptoms above, don’t ignore them. A quick call to a local engineer could mean the difference between a simple fix and a full replacement.